1. Field of the Invention
This invention relates to an IC device inspection apparatus which is capable of evaluating performance of an IC device correctly.
2. Description of the Prior Art
Inspection of temperature characteristics of an IC device is carried out in an environment which is held at a predetermined temperature (thermostatic bath or chamber).
The temperature set point of the chamber is set e.g. at xe2x88x9250xc2x0 C. to +150xc2x0 C. according to inspection programs.
Further, electric current is supplied to the IC device under test in various patterns according to many different test items of an inspection program. As a result, the IC device generates heat by Joule""s law in a different pattern, dependent on the test item. The heat generation is more conspicuous in the case of inspecting an IC device which has a high integration density, such as a microprocessor (NPU) installed in a computer.
In recent years, the processing capacity or speed of microprocessors has been markedly increased, and their integration density has also become higher, resulting in increased watt densities (W/cm2) of such microprocessors under test. Therefore, IC devices including MPUs tend to generate a still larger amount of heat.
For example, when a microprocessor generates approximately 30 watts of heat during inspection, the temperature of the microprocessor becomes higher than the set point temperature of the chamber by 40xc2x0 C. or so.
Further, the amount of heat generated by an IC device becomes larger as the frequency of an electric signal supplied thereto is higher.
Moreover, it is reported that the maximum operating frequency of the microprocessor is lowered with an increase in the temperature of the same due to a lowered switching frequency of transistors, and that if the temperature of the microprocessor rises by 10xc2x0 C., the maximum operating frequency of the same is reduced by 2%.
For example, when the temperature of a microprocessor capable of operating at a maximum operating frequency of 500 MHz becomes 4xc2x0 C. higher than the set point temperature of the chamber, the actual maximum operating frequency of the microprocessor falls by no less than 40 MHz. Therefore, the microprocessor which should be ranked in itself in a class in which operation at 500 MHz is ensured is demoted by one grade or class and ranked as a class of microprocessors for operation at the maximum operating frequency on the order of 400 MHz.
As a result, yields of microprocessors for operation at high operating frequencies are unduly deteriorated, causing a serious loss.
Further, when an IC device undergoes a larger amount of heat generation, it is in danger of destroying itself.
Conventionally, with a view to enhancing accuracy of inspection (i.e. yield of properly ranked IC devices) and preventing self-destruction of IC devices, the temperature of an IC device under test is monitored, whereby the IC device is cooled to the set point temperature of the chamber.
The temperature of an IC device can be measured by a method using a contact temperature sensor such as a thermocouple or a non-contact temperature sensor such as an infrared sensor.
Further, another method can be employed in which a temperature sensor is incorporated in an IC device under test and the temperature of the IC device is measured by is the temperature sensor, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 6-188295.
However, the contact temperature sensor can scratch or soil a package surface of an IC device, causing degradation of the value of the IC device as a commercial product.
On the other hand, the non-contact temperature sensor such as an infrared sensor cannot accurately measure the temperature of an IC device having a metal surface.
Further, the method using the temperature sensor incorporated in the IC device has the inconveniences that the size and weight of the IC device are increased and manufacturing costs of the same are largely increased.
It is an object of the invention to provide an IC device inspection apparatus which is capable of measuring a temperature of an IC device accurately without scratching or soiling the IC device as well as evaluating performance of the IC device correctly even when a temperature sensor is not incorporated in the IC device.
To attain the above object, the present invention provides an IC device inspection apparatus comprising:
a chamber for receiving therein an IC device to be inspected;
an IC tester for judging performance of the IC device;
electrical connection means arranged outside the chamber and having a conductive passage electrically connecting between the IC tester and the IC device;
go an IC socket retained on the electrical connection means, for having the IC device inserted therein;
magnetometric detection means arranged close to the conductive passage of the electrical connection means, for detecting a magnetic field generated when electric current is supplied from the IC tester to the IC device;
temperature control means for controlling a temperature of the IC device; and
control means for controlling the temperature control means based on a signal delivered from the magnetometric detection means, to maintain the temperature of the IC device within a predetermined temperature range.
According to this IC device inspection apparatus, the magnetometric detection means detects the magnetic field which is generated when electric current is supplied from the IC tester via the electrical connection means to the IC device, and varies every moment with the amount of the electric current. The control means controls the temperature control means based on the signal from the magnetometric detection means such that the temperature of the IC device is maintained within a predetermined temperature range.
The electrical connection means is arranged outside the chamber, and the magnetometric detection means is arranged in proximity to the conductive passage of the electrical connection means to thereby keep the magnetometric detection means distant from a source of magnetic noise, so that magnetic noise has little adverse effect on the magnetometric detection means. Further, this arrangement makes it possible to prevent sensing characteristics of the magnetometric detection means from being seriously changed when testing causes an IC device to generate heat to heat itself to high temperatures.
Further, differently from an infrared sensor, the magnetometric detection means is capable of measuring the amount of variation or changes in the temperature of the IC device accurately even when the IC device has a metal surface. Still further, differently from a temperature sensor such as a thermocouple, since the magnetometric detection means is not required to be brought into contact with the IC device, the IC device cannot be scratched or soiled by the magnetometric detection means. Moreover, it is not required to install a temperature sensor in the IC device as in the prior art, so that it is possible to prevent an increase in size and weight of the IC device.
Preferably, the IC device inspection apparatus includes conversion means for converting the signal delivered from the magnetometric detection means to information indicative of an amount of heat generated by the IC device, and the control means controls the temperature control means based on the information from the conversion means, to maintain the temperature of the IC device within the predetermined temperature range.
According to this preferred embodiment, the conversion means converts the signal from the magnetometric detection means to information indicative of an amount of heat generated by the IC device. Based on this information from the conversion means, the control means generates and sends out an instruction responsive to a change in the amount of heat generated by the IC device to the temperature control means, and the temperature control means controls the temperature of the IC device according to the instruction.
More preferably, the temperature control means comprises cold air supply means for supplying a jet of cold air to the IC device, and the control means controls both of a time period over which the jet of cold air is supplied to the IC device and a flow rate of the jet of the cold air, in a feed forward manner based on the information from the conversion means.
Preferably, the chamber has a bottom plate formed with an opening extending therethrough, the IC socket being inserted in the opening, the magnetometric detection means being mounted on an underside of the bottom plate.
Preferably, the electrical connection means comprises a printed circuit board.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with accompanying drawings.